CN113944167B - Settlement calculation method considering soft soil foundation prepressing excavation backfill construction influence - Google Patents
Settlement calculation method considering soft soil foundation prepressing excavation backfill construction influence Download PDFInfo
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Abstract
The invention discloses a settlement calculation method considering the influence of soft soil foundation prepressing excavation backfill construction, which comprises the following steps: analyzing the pre-pressing treatment depth, the load size and the treated consolidation degree of the site, determining the elevation change conditions of the site after pre-pressing, excavating and backfilling construction, respectively adopting linear and nonlinear compression modulus methods to calculate the total consolidation settlement of the filling layer, the residual total consolidation settlement of the soft soil layer caused by backfilling above the pre-pressing treatment depth and the total consolidation settlement of the soft soil layer below the pre-pressing treatment depth, finally calculating the average consolidation degree of the soft soil layer in different stages according to the backfilling process, calculating the total consolidation settlement and the settlement of each stage, and comparing the average consolidation degree with the site monitoring result. Compared with the existing method for considering the complex stress history or calculating the settlement change in the construction process through a finite element tool, the method can be applied to various complex working conditions considering the influence of pre-compaction backfill and excavation, improves the accuracy, is convenient to implement, and can be widely applied to the technical field of constructional engineering.
Description
Technical Field
The invention relates to the technical field of constructional engineering, in particular to a settlement calculation method considering the influence of soft soil foundation prepressing excavation backfill construction.
Background
Engineering on soft ground often requires ground treatment by surcharge or vacuum preloading to increase its ground bearing capacity and reduce settlement. In general, the treatment depth of the foundation needs to reach the bottom of a soft soil layer, but in areas with thick coastal soft soil layers, the foundation cannot be treated to a specified depth, and at the moment, the settlement calculation problem of the soft soil layer in the subsequent excavation and backfilling construction process needs to be considered in a layering manner.
At present, no mature calculation method exists for settlement calculation considering the influence of the soft soil foundation prepressing excavation backfill construction, and the main problem is that the influence of different construction processes on the stress state of the soft soil foundation. For settlement calculation needing to consider complicated stress history, calculation parameters are difficult to obtain, and the stress state of each stage of soil layer cannot be accurately known. When a large finite element tool is used for simulation calculation, the method has certain limitations and is difficult to guide engineering design due to the fact that finite element parameters are numerous, values are difficult to take, and experience and sensitivity are high.
Disclosure of Invention
In view of the above, the invention provides a settlement calculation method considering the influence of soft soil foundation prepressing excavation backfill construction with high accuracy.
The embodiment of the invention determines the elevation change conditions of the site after pre-pressing, excavating and backfilling construction by analyzing the pre-pressing treatment depth, the load size and the treated consolidation degree of the site, respectively adopts a linear and nonlinear compression modulus method to calculate the total consolidation settlement of a filling layer, the residual total consolidation settlement of a soft soil layer caused by backfilling above the pre-pressing treatment depth and the total consolidation settlement of the soft soil layer below the pre-pressing treatment depth, finally calculates the average consolidation degree of the soft soil layer at different stages according to the backfilling process, calculates the total consolidation settlement and the settlement at each stage, and compares the calculation results with the site monitoring results.
The technical scheme provided by the invention is as follows:
a settlement calculation method considering soft soil foundation prepressing excavation backfill construction influence is characterized in that: the method comprises the following steps:
step 1: determining the pre-pressing treatment depth, the load size and the post-treatment consolidation degree of the site, and determining the elevation change condition of the site after pre-pressing, excavation and backfilling construction;
step 2: calculating the total consolidation settlement of the filling layer;
and step 3: calculating the residual total consolidation settlement of the soft soil layer caused by backfilling above the pre-compaction treatment depth;
and 4, step 4: calculating the total consolidation settlement of the soft soil layer below the pre-pressing treatment depth;
and 5: calculating the average consolidation degree of the soft soil layer at different stages according to the backfilling process;
step 6: and calculating the total consolidation settlement and settlement of each stage, comparing with the on-site monitoring result to determine parameters, and recalculating.
Further, the step 1 comprises the following steps:
step 1.1, determining the field prepressing treatment depth to determine settlement calculation soil layer boundary;
step 1.2, determining the size of a pre-pressing treatment load so as to judge the consolidation state of foundation soil in the excavation and backfilling process;
step 1.3, determining the consolidation degree after treatment to calculate the residual total settlement of the soft soil layer caused by backfilling after pre-pressing treatment;
and step 1.4, determining the elevation change condition of the site after pre-pressing, excavating and backfilling construction so as to determine the magnitude of the additional stress acting on the foundation soil.
Further, the step 2 comprises the following steps:
step 2.1, calculating the total thickness of the filling layer, wherein the total thickness of the filling layer is the height from excavation to the bottom surface of the foundation pit to the final backfilled ground;
2.2, selecting proper filling calculation parameters, wherein the filling calculation parameters comprise a settlement calculation empirical coefficient and a compression modulus; the total consolidation settlement is calculated by adopting the compression modulus of the filled soil, and the reduction of the compression modulus value caused by poor filled soil or the improvement of the compression modulus value after layering and rolling needs to be considered;
and 2.3, calculating the total consolidation settlement of the filled soil under the self-weight stress by adopting a compression modulus method without considering the compression amount in the layered rolling construction process.
Furthermore, the calculation formula of the total consolidation settlement of the filling layer in the step 2 is as follows:
in the formula, S 1 Total consolidation settlement of the fill, psi s -calculating the empirical coefficient of sedimentation, E si -compression modulus of the fill, p i Taking the dead weight stress of the fill, h i -total thickness of the fill layer.
Further, the step 3 comprises the following steps:
step 3.1, determining the thickness of the filling layer after pre-pressing and unloading, wherein the soft soil layer above the treatment depth is in a normal consolidation state again;
step 3.2, calculating the consolidation total settlement of the soft soil layer above the treatment depth caused by filling by adopting the nonlinear compression modulus;
and 3.3, calculating the residual total settlement of the soft soil layer above the treatment depth.
Furthermore, the compressive modulus under stress states of different depths is obtained through the e-p curve of the normal consolidated soil, the total consolidated settlement of the treated soft soil layer caused by soil filling is calculated, and the calculation formula is as follows:
E si (σ si )＝a 1 σ si 2 +a 2 σ si +a 3
the residual total settlement is the product of the total consolidation settlement and the residual consolidation degree, and the calculation formula is as follows:
S 2 ＝S 2 ′(1-U 2t )
in the formula, E si (σ si ) -nonlinear compressive modulus, σ, of soft soil layers under different stresses si -vertical stress of the soil layer; a is 1 、a 2 、a 3 -a coefficient; s 2 ' -calculating consolidation total settlement of soft soil layer above treatment depth caused by filling by adopting nonlinear compression modulus psi s -calculating the empirical coefficient of sedimentation, p i -additional stresses causing the soft soil layer to continue to settle; h is i -total thickness of the fill layer; s 2 -total settlement of the soft soil layer residue above the treatment depth, U 2t And actually measuring the consolidation degree of the soft soil layer after pre-pressing treatment.
Furthermore, in the step 4, the influence of pre-pressing loading, unloading and foundation pit excavation on the soft soil layer below the pre-pressing treatment depth is not considered, namely the soft soil layer below the pre-pressing treatment depth is normal consolidated soil, and the additional stress causing consolidation settlement is the backfill soil gravity;
the calculation method adopts a nonlinear compression modulus method, and the calculation formula is as follows:
in the formula, S 3 Soft soil layer Total consolidation Settlement below the Pre-compaction treatment depth, psi s -calculating the empirical coefficient of sedimentation, p i Additional stress, h, causing the soft soil layer to continue to subside i -total thickness of the fill layer;
wherein, E si (σ si ) The calculation formula is as follows:
E si (σ si )＝a 1 σ si 2 +a 2 σ si +a 3
E si (σ si ) -nonlinear compressive modulus, σ, of soft soil layers under different stresses si -vertical stress of the soil layer; a is 1 、a 2 、a 3 -a coefficient.
Further, the step of step 5 is as follows: determining the backfill thickness and the construction gap time of each stage of actual construction, and calculating the average consolidation degree in the backfill process of the soft soil layer by adopting an improved Gao Mujun medium method.
Further, the step of step 6 is as follows:
step 6.1, the total consolidation settlement is the sum of the total consolidation settlement of the fill layer, the remaining total consolidation settlement of the soft soil layer above the pre-pressing treatment depth and the total consolidation settlement of the soft soil layer below the pre-pressing treatment depth, and the calculation formula is as follows:
S＝S 1 +S 2 +S 3
wherein S is 1 For total consolidation settlement of the fill, S 2 For the remaining total consolidation settlement of soft soil layers above the pre-compaction treatment depth, S 3 The soft soil layer is subjected to total consolidation settlement below the pre-pressing treatment depth;
step 6.2, comparing with the field monitoring result, and calibrating the calculation parameter U t The settlement calculation of the influence of soft soil foundation prepressing excavation backfill construction is considered again;
the calibration calculation was performed using the following formula:
S t ＝S·U t
wherein S is t For total consolidation settlement, U, monitored on site t The average consolidation degree of the soft soil layer at different stages.
Further, in the present invention,
the backfilling is large-area backfilling, and the reduction of a limited area is considered for backfilling positions close to a basement structure and the like by adding stress;
ground rebound caused by prepressing and unloading is not considered in calculation;
foundation and upper structure construction is immediately carried out after the foundation pit is assumed to be excavated, and foundation springback caused by excavation of the foundation pit is not considered;
compared with the soft soil layer below the prepressing treatment depth, the residual total settlement of the soft soil layer above the prepressing treatment depth can be completed within a period of time after the soft soil layer is backfilled to the designed elevation;
when a linear compression modulus method is adopted, the sedimentation empirical coefficient is 1.5; when the nonlinear compression modulus method is employed, the empirical coefficient of sedimentation is 1.0.
The invention has the following beneficial effects:
(1) Compared with the existing method for considering the complex stress history or calculating the settlement change in the construction process through a finite element tool, the method can be applied to various complex working conditions considering the influence of pre-compaction backfill and excavation, improves the accuracy and is convenient to implement.
(2) The calculation method disclosed by the invention is clear in mechanical concept, simple and convenient in calculation, stable in calculation result, reliable and simple, solves the problems of complicated settlement calculation and unreliable result considering the influence of the pre-pressing excavation backfill construction, and provides an effective, simple and convenient practical calculation method for soft soil foundation settlement under the complex construction working condition of actual engineering calculation.
Drawings
FIG. 1 is a flow chart of the steps of an embodiment of the present invention;
FIG. 2 is a calculation chart of the total consolidation settlement of the soft soil layer caused by backfilling above the total consolidation settlement and the pre-compaction treatment depth of the fill layer and the total consolidation settlement of the soft soil layer below the pre-compaction treatment depth;
FIG. 3 is a graph of the present invention illustrating the stacking versus time and consolidation versus time;
FIG. 4 is a graph comparing the calculated settlement at each stage of the construction with the actual measurement monitoring result at the site;
fig. 5 is a soft soil layer e-p curve.
Detailed Description
The invention will be further explained and explained with reference to the drawings and the embodiments in the description. The step numbers in the embodiments of the present invention are set for convenience of illustration only, the order between the steps is not limited at all, and the execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.
Examples
Referring to fig. 1, an embodiment of the present invention provides a settlement calculation method considering the influence of soft soil foundation pre-compaction excavation backfill construction, including the following steps:
step 1: determining the pre-pressing treatment depth, the load size and the post-treatment consolidation degree of the site, and determining the elevation change condition of the site after pre-pressing, excavation and backfilling construction;
step 2: calculating the total consolidation settlement of the filling layer;
and step 3: calculating the residual total consolidation settlement of the soft soil layer caused by backfilling above the pre-pressing treatment depth;
and 4, step 4: calculating the total consolidation settlement of the soft soil layer below the pre-pressing treatment depth;
and 5: calculating the average consolidation degree of the soft soil layer at different stages according to the backfilling process;
and 6: calculating the total consolidation settlement and settlement of each stage, comparing with a field monitoring result to determine parameters, and recalculating;
specifically, the step 1 includes the following steps:
1.1, determining the field prepressing treatment depth to determine settlement calculation soil layer boundary;
1.2, determining the size of the pre-pressing treatment load so as to judge the consolidation state of the foundation soil in the excavation and backfilling process;
1.3, determining the consolidation degree after treatment to calculate the residual total settlement of the soft soil layer caused by backfilling after pre-pressing treatment;
1.4, determining the elevation change condition of the site after pre-pressing, excavating and backfilling construction so as to determine the magnitude of additional stress acting on foundation soil;
specifically, the step 2 includes the following steps:
2.1, calculating the total thickness of the filling layer, wherein the total thickness of the filling layer is the height from excavation to the bottom surface of the foundation pit to the final backfilled ground;
2.2 selecting proper filling calculation parameters, wherein the calculation parameters comprise a settlement calculation empirical coefficient and a compression modulus; the total consolidation settlement is calculated by adopting the compression modulus of the filled soil, and the reduction of the compression modulus value caused by poor filled soil or the improvement of the compression modulus value after layering and rolling needs to be considered;
2.3 calculating the total consolidation settlement of the filling layer;
calculating the total consolidation settlement of the filling layer, wherein the total consolidation settlement of the filling under the dead-weight stress is calculated by adopting a compression modulus method without considering the compression amount in the layered rolling construction process, and the calculation formula is as follows:
in the formula, S 1 Total consolidation settlement of the fill, psi s -calculating the empirical coefficient of sedimentation, E si -compression modulus of the fill, p i Taking the dead weight stress of the fill, h i -total thickness of the fill layer;
specifically, the step 3 includes the following steps:
3.1 determining the thickness of the filling layer after pre-pressing and unloading, and enabling the soft soil layer above the treatment depth to be in a normal consolidation state again;
3.2 calculating the consolidation total settlement of the soft soil layer above the treatment depth caused by filling by adopting the nonlinear compression modulus;
3.3 calculating the residual total settlement of the soft soil layer above the treatment depth.
As shown in fig. 2, when the additional stress caused by the backfill reaches the pre-compaction pressure, the soft soil above the treatment depth continues to settle at the backfill height;
and (3) solving the compression modulus under different depth stress states through a normal consolidated soil e-p curve, and calculating the total consolidated settlement of the treated soft soil layer caused by soil filling, wherein the calculation formula is as follows:
E si (σ si )＝a 1 σ si 2 +a 2 σ si +a 3
the residual total settlement is the product of the total consolidation settlement and the residual consolidation degree, and the calculation formula is as follows:
S 2 ＝S 2 ′(1-U 2t )
in the formula, E si (σ si ) -nonlinear compressive modulus, σ, of soft soil layers under different stresses si -vertical stress of the soil layer; a is 1 、a 2 、a 3 -a coefficient; s. the 2 ' calculating the total settlement of consolidation of soft soil layer above the treatment depth caused by filling by adopting nonlinear compression modulus psi s -calculating the empirical coefficient of sedimentation, p i Additional stress, h, causing the soft soil layer to continue to subside i -total thickness of the fill layer; s. the 2 -total settlement of the soft soil layer residue above the treatment depth, U 2t And actually measuring the consolidation degree of the soft soil layer after pre-pressing treatment.
Specifically, in the step 4, the influence of the pre-compaction loading, unloading and foundation pit excavation on the soft soil layer below the pre-compaction treatment depth is not considered, namely the soft soil layer below the pre-compaction treatment depth is normal consolidated soil, the additional stress causing the consolidation settlement is the backfill soil gravity, the calculation method adopts a nonlinear compression modulus method, and the calculation formula is as follows:
in the formula, S 3 Soft soil layer Total consolidation Settlement below the Pre-compaction treatment depth, psi s -calculating an empirical factor, p, for the sedimentation i Additional stress, h, causing the soft soil layer to continue to subside i -total thickness of the fill layer;
wherein E is si (σ si ) The calculation formula is as follows:
E si (σ si )＝a 1 σ si 2 +a 2 σ si +a 3
E si (σ si ) -nonlinear compression modulus, σ, of soft soil layers under different stress conditions si -vertical stress of the soil layer; a is a 1 、a 2 、a 3 -a coefficient.
Specifically, in the step 5, as shown in fig. 3, the backfill soil thickness and the construction gap time at each stage of actual construction are determined, and the average consolidation degree in the soft soil layer backfilling process is calculated by adopting an improved Gao Mujun medium method.
Specifically, the step 6, as shown in fig. 4, includes the following steps:
6.1 the total consolidation settlement is equal to the sum of the total consolidation settlement of the filling layer, the remaining total consolidation settlement of the soft soil layer above the prepressing treatment depth and the total consolidation settlement of the soft soil layer below the prepressing treatment depth, and the calculation formula is as follows:
S＝S 1 +S 2 +S 3
wherein S is 1 For total consolidation settlement of the fill, S 2 For the remaining total consolidation settlement of soft soil layers above the pre-compaction treatment depth, S 3 The soft soil layer is subjected to total consolidation settlement below the pre-pressing treatment depth;
6.2 comparing with the on-site monitoring result to calibrate the calculation parameter U t Carrying out settlement calculation considering the influence of the soft soil foundation prepressing excavation backfill construction again;
the calibration calculation was performed using the following formula:
S t ＝S·U t
wherein S is t For total consolidation settlement, U, monitored in situ t The average consolidation degree of the soft soil layer at different stages.
Taking the calculation of the total settlement after the pre-pressing, the excavation of the foundation pit and the backfilling of the foundation of an office building on the soft soil foundation as an example, the pre-pressing treatment depth is known to be 18m, and the soft soil layer with the depth of 13.5m is still remained below the treatment depth. The ground elevation of the field after vacuum preloading treatment is 1.5m, the foundation pit is excavated until the elevation of the pit bottom is-3.75 m, the fertilizer tank of the foundation pit is backfilled to +2.45m, the soil is backfilled to +4.95m for the second time, and finally the field elevation is backfilled to + 5.40- +5.72m through gardens and roads.
Detailed description the concrete implementation steps of the settlement calculation method considering the influence of the soft soil foundation prepressing excavation backfill construction are as follows:
(1) And according to the pre-pressing treatment depth, dividing the whole foundation into three layers of soil for calculation, wherein the three layers of soil are respectively a fill layer, a soft soil layer above the pre-pressing treatment depth and a soft soil layer below the treatment depth. Determining the thickness of the backfill settlement to be 6.1m by taking the excavation bottom elevation of the foundation pit as a standard; and determining the thickness of the filling soil for causing the consolidation and settlement of the lower horizontal soft soil layer to be 3.85m based on the elevation of 1.5m of the ground of the field after the vacuum preloading treatment. When the backfill thickness reaches 3.85m, the lower lying soft soil layer is in a normal consolidation state.
(2) And (5) taking the compression modulus Es =10MPa of the filling layer, and calculating the self-sedimentation of the filling under the self-weight.
S 1 ＝18.5×6.10/2×6.10/10＝34.4mm。
(3) According to the soft soil layer e-p curve, as shown in figure 5.
Calculating the nonlinear relation between the vertical stress sigmaz and the compressive modulus Es as follows:
E s (σ z )＝-0.000005σ z 2 +0.0115σ z +0.0112
the layered thickness is 1.0m, and the nonlinear compression modulus results of the upper and lower soft soil layers in the pre-pressing treatment depth are calculated as follows:
calculating the total consolidation settlement of the soft soil layer above the pre-pressing treatment depth by adopting the upper surface nonlinear compression modulus: s 2 =126.1mm, the average value of the soft soil consolidation degree after the field actual measurement pre-pressing treatment is 85%, so that the soft soil layer residual total consolidation settlement above the pre-pressing treatment depth is as follows: s 2 ＝126.1×(1-85％)＝18.9mm。
(4) And (3) calculating, namely calculating the total consolidation settlement of the soft soil layer with the pre-compaction treatment depth below by adopting a nonlinear compression modulus: s 3 ＝713.4mm；
(5) An improved Gao Mujun medium method is adopted to calculate an average consolidation degree curve in the soft soil layer backfilling process, and the calculation parameters and the process are as follows:
| soil series | Severe gamma/kN m-3 | Thickness/m | Permeability coefficient kv/cm/s | Compression modulus Es/MPa |
| Soft soil layer with more than depth of prepressing treatment | 16.8 | 15.8 | - | - |
| Soft soil layer below prepressing treatment depth | 16 | 13.5 | 1.32×10 -7 | 1.9 |
For the treated sludge, the residual sedimentation amount is supposed to be completed within a period of time after the stacking is completed.
For the sludge which is not pre-pressed and is treated in the lower horizontal position, the calculation parameters in the formula are as follows:
α＝8/π 2 ＝0.8106；
C v ＝k v E s1 /γ w ＝0.0217
β＝π 2 ×C v /4H 2 ＝0.00117
in the embodiment, the backfill work is started after the foundation pit is excavated to the pit bottom elevation in 7 months in 2017, and the backfill construction process at the section 1 is calculated as follows:
(1) 3-7 months in 2017, designing the elevation of a foundation pit slope-laying excavation bottom to be-3.75 m;
(2) 11-12 months in 2017, backfilling the foundation pit fertilizer groove from +1.50m to +2.45m;
(3) 5-7 months in 2018, and backfilling the foundation pit to +4.95m for the second time;
(4) 10-11 months in 2018, and backfilling the garden to a height of +5.35m;
calculating the average consolidation degree of the soft soil layer in different stages according to the excavation and backfilling process, wherein the calculation result is shown in figure 3;
(6) The total consolidation settlement is equal to the sum of the total consolidation settlement of the fill layer, the remaining total consolidation settlement of the soft soil layer above the pre-pressing treatment depth and the total consolidation settlement of the soft soil layer below the pre-pressing treatment depth: s = S 1 +S 2 +S 3 ＝873.9mm；
The calculated settlement results and the actual measurement results at each stage are shown in figure 4.
From the calculation results in the step (6), the total settlement calculated by the settlement calculation method considering the influence of the pre-compaction excavation backfill construction, the settlement calculation results of each construction stage are more consistent with the field actual measurement results, and the calibration of the calculation parameters can be carried out on the deviated actual measurement points to carry out the recalculation.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (5)
1. A settlement calculation method considering soft soil foundation prepressing excavation backfill construction influence is characterized in that: the method comprises the following steps:
step 1: determining the pre-pressing treatment depth, the load size and the treated consolidation degree of the field, and determining the elevation change condition of the field after pre-pressing, excavation and backfilling construction;
step 2: calculating the total consolidation settlement of the filling layer;
and step 3: calculating the remaining total consolidation settlement of the soft soil layer caused by backfilling above the pre-compaction treatment depth, and comprising the following steps of:
step 3.1, determining the thickness of the filling layer after pre-pressing and unloading, wherein the soft soil layer above the treatment depth is in a normal consolidation state again;
step 3.2, calculating the consolidation total settlement of the soft soil layer above the treatment depth caused by filling by adopting the nonlinear compression modulus;
3.3, calculating the residual total consolidation settlement of the soft soil layer above the treatment depth;
and (3) solving the compression modulus under different depth stress states through a normal consolidated soil e-p curve, and calculating the total consolidated settlement of the treated soft soil layer caused by soil filling, wherein the calculation formula is as follows:
the residual total consolidation settlement is the product of the total consolidation settlement and the residual consolidation degree, and the calculation formula is as follows:
in the formula (I), the compound is shown in the specification,
the nonlinear compression modulus of the soft soil layer under different stresses,
-vertical stress of the soil layer; a is 1 、a 2 、a 3 -the number of coefficients is,
calculating the consolidation total settlement of the soft soil layer above the treatment depth caused by filling by adopting the nonlinear compression modulus,
-calculating the empirical coefficients of the sedimentation,
-additional stresses causing the soft soil layer to continue to settle,
-total thickness of the fill layer;
-the remaining total sedimentation of the soft soil layer above the treatment depth,
actually measuring the consolidation degree of the soft soil layer after the prepressing treatment;
and 4, step 4: calculating the total consolidation settlement of the soft soil layer below the pre-pressing treatment depth;
in the step 4, the influence of pre-pressing loading, unloading and foundation pit excavation on a soft soil layer below the pre-pressing treatment depth is not considered, namely the soft soil layer below the pre-pressing treatment depth is normal consolidated soil, and the additional stress causing consolidation settlement is the backfill soil gravity; the calculation method adopts a nonlinear compression modulus method, and the calculation formula is as follows:
in the formula (I), the compound is shown in the specification,
the soft soil layer below the pre-pressing treatment depth is totally consolidated and settled,
-calculating the empirical coefficients of the sedimentation,
-additional stresses causing the soft soil layer to continue to settle,
-total thickness of the fill layer;
wherein the content of the first and second substances,
the calculation formula is as follows:
and 5: calculating the average consolidation degree of the soft soil layer at different stages according to the backfilling process;
step 6: the method comprises the following steps of calculating total consolidation settlement and settlement of each stage, comparing with a field monitoring result to determine parameters, and recalculating, wherein the recalculating comprises the following steps:
step 6.1, the total consolidation settlement is the sum of the total consolidation settlement of the fill layer, the remaining total consolidation settlement of the soft soil layer above the pre-pressing treatment depth and the total consolidation settlement of the soft soil layer below the pre-pressing treatment depth, and the calculation formula is as follows:
wherein, the first and the second end of the pipe are connected with each other,S 1 in order to realize the total consolidation and settlement of the filling layer,S 2 for the remaining total consolidation settlement of the soft soil layer above the pre-compaction treatment depth,S 3 the soft soil layer is subjected to total consolidation settlement below the pre-pressing treatment depth;
step 6.2, comparing with the field monitoring result, and calibrating the calculation parametersU t The settlement calculation of the influence of the soft soil foundation prepressing excavation backfill construction is considered again;
the calibration calculation was performed using the following formula:
wherein the content of the first and second substances,S t for the total consolidation settlement monitored on site,U t the average consolidation degree of the soft soil layer at different stages is obtained;
in the method, the backfilling is large-area backfilling, and the reduction of a limited area is considered for backfilling near a basement structure and the like by adding stress;
ground rebound caused by prepressing and unloading is not considered in calculation;
foundation and superstructure construction is immediately carried out after foundation pit excavation is assumed, and foundation springback caused by foundation pit excavation is not considered;
compared with the soft soil layer below the prepressing treatment depth, the residual total settlement of the soft soil layer above the prepressing treatment depth can be completed within a period of time after the soft soil layer is backfilled to the designed elevation;
when a linear compression modulus method is adopted, the sedimentation empirical coefficient is 1.5; when the nonlinear compression modulus method is employed, the empirical coefficient of sedimentation is 1.0.
2. The method according to claim 1, wherein the step 1 comprises the steps of:
step 1.1, determining the field prepressing treatment depth to determine settlement calculation soil layer boundary;
step 1.2, determining the size of a pre-pressing treatment load so as to judge the consolidation state of foundation soil in the excavation and backfilling process;
step 1.3, determining the consolidation degree after treatment to calculate the residual total settlement of the soft soil layer caused by backfilling after pre-pressing treatment;
and step 1.4, determining the elevation change condition of the site after pre-pressing, excavating and backfilling construction so as to determine the magnitude of the additional stress acting on the foundation soil.
3. The method according to claim 1, wherein said step 2 comprises the steps of:
step 2.1, calculating the total thickness of the filling layer, wherein the total thickness of the filling layer is the height from excavation to the bottom surface of the foundation pit to the final backfilled ground;
2.2, selecting proper filling calculation parameters, wherein the filling calculation parameters comprise a settlement calculation empirical coefficient and a compression modulus;
and 2.3, calculating the total consolidation settlement of the filling layer of the filling under the dead weight stress by adopting a compression modulus method without considering the compression amount in the layered rolling construction process.
4. The method of claim 3 wherein the total consolidated settlement of the fill is calculated by the formula:
in the formula, S 1 -the total consolidation settlement of the fill layer,
-calculating the empirical coefficients of the sedimentation,
-the compression modulus of the fill layer,
-taking the dead weight stress of the fill layer,
-total thickness of the fill layer.
5. The method of claim 1, wherein the step of step 5 is as follows: and determining the backfill thickness and the construction clearance time in each stage of actual construction, and calculating the average consolidation degree in the backfill process of the soft soil layer by adopting an improved Gao Mujun dielectric method.
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